The present invention generally pertains to hollow, stackable, molded plastic products and is particularly directed to enhancing the rigidity of such products.
Hollow, stackable, molded plastic products, such as beverage cups, typically have tapered perimetric side walls. Typically, the permetric side walls are circumferential. The side walls are tapered so that the products may be stacked by inserting one product into another. Each product has a given stacking height defined by the height that a product when inserted into a like product extends beyond the height of the like product. The stacking height for a given product is determined by physical features of the product that cause the inserted product to contact the like receiving product to limit the dimension of product insertion. The "stacking height" for a given product is the difference in height between the top of one said given product and the top of another said given product stacked within the one said given product. Typically, the inserted end of the inserted product contacts an interior ridge or some other interior protrusion near the base of the like receiving product to limit the dimension of product insertion; and the stacking height is such in relation to the tapering of the side walls and the height of the product as to prevent the side walls of the inserted product from so closely contacting the side walls of the like receiving product as to tend to bind the products together when they are stacked.
As injection molding techniques have evolved, hollow, stackable, injection-molded plastic products have been made with thinner side walls in order to conserve plastic and thereby decrease the material cost of the product. As the side walls have become thinner it has become desirable to enhance the rigidity of the product. Rigidity has been enhanced by providing a series of steps in the perimetric tapered side walls. Typically, each step is defined by a combination of a ledge; a first perimetric side wall generally extending from the ledge in a first direction; and a second perimetric side wall spaced from the first perimetric side wall by the ledge and extending from the ledge in a direction generally opposite from the first direction, wherein at the ledge the cross-sectional area of the first perimetric side wall is greater than the cross-sectional area of the second perimetric side wall.
In one such product configured as a generally cylindrical container having slightly tapered circumferential side walls, a base and an open top, the rigidity of the top portion of the product closer to the widest end of the product than the stacking height of the product is enhanced by the combination of a circumferential ledge joining the upper and lower circumferential side walls near the top of the product and a skirt-shaped circumferential flange extending from the ledge. The skirt-shaped flange is outside of and spaced from the lower circumferential side wall, and extends from the ledge in a direction away from the top of the product.